In recent years, lithium ion batteries, nickel hydrogen batteries, and other secondary batteries are growing in importance as power supplies for vehicles, personal computers, and portable terminals. In particular, lithium secondary batteries have a light weight and a high energy density, and thus are suitable as a high-output power supplies for vehicles. A lithium secondary battery includes positive and negative electrodes each containing a material (active material) reversibly stores and releases lithium ions (Li ions), and is charged and discharged by the migration of Li ions between the positive and the negative electrodes.
Typical examples of the active material contained in a positive electrode of a lithium secondary battery (positive electrode active material) includes a lithium transition metal oxide containing lithium and a transition metal element. A preferred example is a lithium transition metal oxide containing at least nickel (Ni) as the transition metal element (nickel-containing lithium transition metal oxide) having a layered structure. The lithium transition metal oxide has low electron conductivity, and thus is normally used in the form of a mixture with an electrically conductive material such as carbon powder, Patent Literature 1 is a technical literature relating to the active materials and electrically conductive materials of lithium secondary batteries.